I just looked up Wikipedia to find out if there was a difference in the description between Dandelion and milkweed but both are described as having milky sap…

About milkweed it says :

“Milkweeds use three primary defenses to limit damage caused by caterpillars: hairs on the leaves, cardenolide toxins, and latex fluids. Data from a DNA study indicate that more recently evolved milkweed species use these preventative strategies less but grow faster than older species, potentially regrowing faster than caterpillars can consume them”

Now getting back to your original question … Sometimes I find on a hot day and when the plant is dry the smell gives me headaches. So possibly you do have a swan plant there Best to take a photo and put the photo on Plant ID NZ on Facebook